1. Field of the Invention
The present invention relates to single propellant gas generators. More specifically, the invention is an energetic ionic liquid monopropellant; a gas generator comprising the energetic ionic liquid monopropellant and a metal catalyst; and a method for generating a gas in which an energetic ionic liquid monopropellant is contacted with a metal catalyst.
2. Description of Related Art
In a catalytic, monopropellant gas generator, a monopropellant is contacted with a catalyst that causes the monopropellant to rapidly decompose, usually without causing monopropellant combustion. Hot gas produced by the catalytic decomposition of a monopropellant may be used, for example, to drive a turbine of an emergency generator providing electricity. Combustion of the monopropellant in a gas generator must normally be avoided because combustion temperatures are high enough to irreversibly inactivate the catalyst and/or damage the gas generator and/or the turbine. Therefore, combinations of monopropellant, catalyst, and operating conditions are desired that rapidly produce large amounts of hot gas without ignition.
Monopropellant gas generators based on hydrazine and iridium catalyst are described in U.S. Pat. No. 3,871,828; U.S. Pat. No. 4,324,096; and U.S. Pat. No. 4,490,972. Hydrazine is a powerful but toxic and volatile monopropellant. Less toxic and/or less volatile alternatives to hydrazine monopropellant, including some ionic liquids, have been made. These ionic liquids are not useful for many existing gas generator applications, however, because of poor thermal stability or failure to perform as expected under required operating conditions. Consequently, there remains a need in the art for a reliable gas generator using a less toxic and/or less volatile alternative to hydrazine.
U.S. Pat. No. 6,218,577 to Brand et al. discloses the synthesis of specific energetic, hydrazinium salts, including hydroxyethylhydrazinium (HEH) nitrate salts and indicates that the salts are useful as a replacement for hydroxylammonium nitrate (HAN) in monopropellant fuels for propulsion and gas generators. The '577 patent does not provide any examples of or conditions required for the use of HEH nitrate salt monopropellant.
U.S. Pat. No. 5,485,722 to Schmidt et al. discloses the catalytic decomposition of HAN by platinum group or transition metal group catalysts including 32% iridium on alumina, 12% rhodium on alumina, 10% platinum on alumina, 12% ruthenium on alumina, and platinum/titanium sheet catalyst. The '722 patent discloses that the controlled catalytic HAN decomposition is preferably conducted at a temperature of between 80° C. and 120° C. The rate of HAN decomposition is controlled and combustion and detonation of HAN requires choking of the exit flow from a reactor in a sonic flow nozzle as well as controlling the flow of monopropellant over the catalyst.
U.S. Pat. No. 7,745,635 to Drake et al. and U.S. Pat. No. 6,509,473 to Drake disclose energetic ionic liquids including 4-amino-1,2,4-triazolium nitrate and that the energetic ionic liquids should have applications as monopropellants and gas generators. The '635 patent makes no mention of catalytic decomposition or conditions under which 4-amino-1,2,4-triazolium salts might be used as catalytic decomposition monopropellants.
US 2005/0269001 discloses energetic ionic liquids useful as monopropellants for propulsion and gas generators but does not mention catalysts or conditions for the use of any energetic ionic liquids for gas generation.